'Castle' star Stana Katic: 'Caskett fans will be very pleased by the end of the season.' Plus, more scoop! -- EW VIDEO

The March 19 episode of Castle, screened tonight for a packed theater during PaleyFest in Los Angeles, has all the things that make a great standalone hour.

There’s a mind-bending case (involving a murder at a Dancing With the Stars-esque show), some hilarious interactions between Ryan (Seamus Dever) and Esposito (Jon Huertas), a few great scenes involving Martha (Susan Sullivan) and a rival from her past, and, of course, a revealing moment or two between one of TV’s best sort-of couples, Castle (Nathan Fillion) and Beckett (Stana Katic). But executive producer and creator Andrew Marlowe had a warning for the crowd before he showed the episode: Take some time to bask in the familiar lightness of the episode – because things are going to get heavy. “[It’s] the last normal episode before the story weather hits,” he said during his introduction. Gulp.

Of course, that’s pretty much how Castle operates every year, but this season, more than ever, has played with the build up between Castle and Beckett. At the end of last season, Castle whispered to injured Kate that he loved her and neither party has addressed it since. (Castle is under the impression she didn’t hear it, but the audience knows that is not true.)

So will the end of the season bring around the payoff fans have been seeking? You bet, says Marlowe. “This has been a season of secrets. Castle and Beckett are both keeping significant secrets from each other…and they start to come out. And both characters – and all the characters around them – will have to deal with the emotional consequences of it,” he said. “We’re really looking forward to bringing those episodes to life. We think it will be a lot of fun for loyal fans of the show to see these characters tested.”

In fact, before the event, Stana Katic confidently said that fans of the pairing won’t be disappointed with the outcome the show has in store. “Caskett fans will be very pleased by the end of the season,” she said coyly. And for anyone that follows casting news, that promise holds even greater value now that we know Spartacus hottie Brett Tucker, who will come on board for an episode, won’t pose a serious threat. (But for more on his guest spot, see our chat with Katic below:)

Other scoop:
+ Marlowe also shared that Beckett’s mother’s murder would be addressed again before the end of the season, and that they’re in no rush to dig deeper into the truth behind Castle’s dad (who was revealed to be a former CIA agent in the recent two-parter episode).
+ Fillion will soon film with Firefly co-star Adam Baldwin, who will play Det. Ethan Slaughter, and is excited about the reunion. He warned, however: “I think it’s safe to say parts of [Castle’s] face will be re-arranged.”
+ In more ominous news, Marlowe could not say for sure that Molly Quinn, whose character is in the process of deciding her next step, would return next season. But if we had to bet, we’d say it’s quite likely.
+ One thing we refused to bet on? When Castle and Beckett will finally dive into a real relationship. Marlowe promises it will happen at some point before the end of the series – and he knows exactly when. But good luck getting anything out of him!